Force measuring joint distraction lever

ABSTRACT

A method for assessing a joint includes inserting a joint distraction lever into a space between a first bone and a second bone of the joint, distracting the joint with the joint distraction lever, determining, using a measurement device of the joint distraction lever, a distraction force applied by the joint distraction lever as the joint distraction lever is used to distract the joint, determining whether the distraction force matches a predetermined amount of the distraction force, and in response to determining that the distraction force matches the predetermined amount of the distraction force, capturing first poses of the first bone and the second bone.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 14/724,381, filed May 28, 2015, which claims the benefit of andpriority to U.S. Provisional Patent Application No. 62/004,015, filedMay 28, 2014 and titled “Force Measuring Joint Distraction Lever,” theentireties of which are incorporated by reference herein.

BACKGROUND

The present invention relates generally to the field of surgical toolsfor use during planning and preparation of a joint replacementprocedure, and more particularly to a force measuring lever for useduring joint distraction.

Over time, as a result of disease, injury, or longevity of use, bones ofa joint may degenerate, resulting in pain and diminished functionality.To reduce pain and restore functionality, a joint replacement proceduremay be necessary. Examples of such procedures may be total or partialknee arthroplasty, total hip arthroplasty, or knee or hip resurfacing.In these procedures, portions of a patient's joint are replaced withartificial components. Particularly, a surgeon uses a surgical cuttingtool to remove portions of bone to prepare the bone to receive aprosthetic device. Prior to resection of the bone, the surgeon plansbone preparation specific to the patient's anatomy, size, current stateof the target joint, and several other factors in order to determine theportions of the bone that will be removed and replaced by one or moreprosthetic components, as well as to determine proper positioning of theone or more prosthetic components.

One step of surgical planning for a partial knee resurfacing procedureinvolves a knee joint distraction, that is, forced separation of thedistal femur from the proximal tibia. For partial knee resurfacing, thisis intended to correct knee joint deformity and cause properre-tensioning of the ligaments of the knee to determine a desired,post-procedure joint construction. In one exemplary method, prior toresection and prior to a creating a final implant plan, the knee jointdeformity is corrected at multiple flexion positions or flexion anglesby distracting the joint. An instantaneous six degree-of-freedom (DOF)position (i.e. the pose) of the femur with respect to the six DOFposition of the tibia is captured at each of the multiple flexionpositions. For example, a common flexion position is near full extensionwhere the surgeon applies a valgus torque to the tibia when the leg isat approximately 5-10 degrees of flexion. The valgus torque corrects thelimb alignment deformity and returns the ligaments to a proper tensionstate. Another common flexion position is 90 degrees flexion. With thesetwo poses, the knee joint is in the desired post-resection finalposition. After collection of poses, bone resection, implantpositioning, and implant characteristics are planned so as to maintainthis relative alignment by making the femoral and tibial componentscontact (or be slightly gapped to allow for some laxity). Once the boneis resected at this desired plan and the trials and/or implants aresecured to the bone, the leg will then be in the pre-resected posedpositions.

A first technique currently used to apply a joint distraction forceincludes manually applying a valgus torque (for a varus knee) to thetibia portion of a patient's leg to pivot the knee joint about thecontralateral compartment (lateral compartment for a varus knee).Another technique includes applying a distraction force using a commonsurgical osteotome by levering the osteotome off the front of the tibiaand lifting the femur vertically. Similarly, joint distraction may beperformed by placing shim-like spoons or gap sticks between the femurand tibia, or by using laminar spreaders to create the distance betweenthe femur and the tibia.

However, for each of these techniques, the “proper” joint distractionforce is subjective, varies from surgeon-to-surgeon, and is difficultfor surgeons to learn. In addition, for the first technique describedabove, applying a valgus torque to the tibia for any pose after 30degrees flexion is extremely difficult because the femur tends to rotateabout the femoral head.

Other types of distractors include spring-based, electromechanical, orhydraulic opposing plate spreaders. However, these tend to be large andcomplex, and due to their size generally require at least some bone tobe removed first (provisional resection) to accommodate the device'sopposing plates. Yet another device is a force sensing shim. However,like the shim-like spoons or gap sticks, this device generally requiresiteratively inserting the device into the joint with various thicknessesuntil the desired force is achieved, making it time consuming andcumbersome.

SUMMARY

According to one aspect, the present disclosure is directed to a jointdistraction lever, having a lever body having a handle portion and aworking portion. The lever body includes a fulcrum extending from abottom surface of the working portion of the lever body and a distaltip, wherein the distal tip is raised above a top surface of the workingportion of the lever body. The joint distraction lever is configured tomeasure a distraction force applied at the distal tip during adistraction procedure when a torque is applied by an external forceapplied on the handle portion of the lever body. The joint distractionlever further includes an indicator configured to provide feedbackrelated to the distraction force applied at the distal tip, as measuredby the joint distraction lever.

According to another aspect, the present disclosure is directed to amethod for performing joint distraction that includes moving a jointincluding a first bone and a second bone into a first flexion positionand inserting a joint distraction lever into the space between the firstbone and the second bone. The joint distraction lever includes a leverbody having a handle portion and a working portion, a fulcrum extendingfrom a bottom surface of the working portion of the lever body, and adistal tip, wherein the distal tip is raised above a top surface of theworking portion of the lever body. The joint distraction lever furtherincludes a force measurement device configured to measure a distractionforce applied at the distal tip during a distraction procedure when atorque is applied by an external force applied on the handle portion ofthe lever body. The joint distraction lever further includes anindicator configured to demonstrate the distraction force applied at thedistal tip, as measured by the joint distraction lever. The methodfurther includes applying a force to the handle portion of the leverbody of the joint distraction lever to cause a torque on the jointdistraction lever and receiving feedback from the indicator related tothe amount of distraction force being applied to the first bone at thedistal tip.

According to another aspect, the present disclosure is directed to aninstrumented osteotome including a lever body having a handle portionand a working portion. A fulcrum extends from a bottom surface of theworking portion of the lever body and a distal tip is raised above a topsurface of the working portion of the lever body. The osteotome furtherincludes a strain gauge for measuring a stress on the lever body todetermine a distraction force applied at the distal tip, and a powersource for providing voltage to the strain gauge. The osteotome alsoincludes a display electrically coupled to the output of the straingauge and configured to provide feedback related to the distractionforce applied at the distal tip, as measured by the strain gauge. Thedisplay is further configured to be in a first state when a firstdistraction force is applied and to be in a second state when a seconddistraction force is applied.

The invention is capable of other embodiments and of being practiced orbeing carried out in various ways. Alternative exemplary embodimentsrelate to other features and combinations of features as may begenerally recited in the claims.

BRIEF DESCRIPTION OF THE FIGURES

The invention will become more fully understood from the followingdetailed description, taken in conjunction with the accompanyingdrawings, wherein like reference numerals refer to like elements, inwhich:

FIG. 1 is a top side view of a joint distraction lever according to afirst exemplary embodiment.

FIG. 2A is a lateral side view of the joint distraction lever of FIG. 1.

FIG. 2B is a lateral side view of a joint distraction lever according toanother exemplary embodiment.

FIG. 2C is a second lateral side view of the joint distraction lever ofFIG. 2B.

FIG. 3A is a bottom side view of the joint distraction lever of FIG. 1.

FIG. 3B is a bottom side view of a joint distraction lever according toanother exemplary embodiment.

FIG. 3C is a bottom side view of the joint distraction lever of FIG. 2B.

FIG. 4 depicts joint distraction of a patient's knee joint using thejoint distraction lever of FIG. 1.

FIG. 5 depicts a closer view of joint distraction of a patient's kneejoint using the joint distraction lever of FIG. 1.

FIG. 6 depicts joint distraction of a patient's knee joint using a jointdistraction lever according to another exemplary embodiment.

FIGS. 7A-7C depict joint distraction of a patient's knee joint using ajoint distraction lever having an indicator according to an exemplaryembodiment.

FIG. 8 illustrates one embodiment of a method for performing jointdistraction using a joint distraction lever according to an exemplaryembodiment.

FIG. 9 illustrates a surgical system with which a joint distractionlever according to an exemplary embodiment may be used.

DETAILED DESCRIPTION

Before turning to the figures, which illustrate the exemplaryembodiments in detail, it should be understood that the application isnot limited to the details or methodology set forth in the descriptionor illustrated in the figures. It should also be understood that theterminology is for the purpose of description only and should not beregarded as limiting.

Referring to FIGS. 1-3, a joint distraction lever is shown. In certainembodiments, the joint distraction lever is an osteotome 10. Though thepresent description will refer to the joint distraction lever as theosteotome 10, it is to be understood that the features disclosed hereinmay be used with and provided in a variety of lever-type devices, whichare considered to be within the scope of the present disclosure. Asshown in FIGS. 1-3, the various embodiments of osteotome 10 include alever body 12 having a handle portion 14 and a working portion 16. Afulcrum 18 extends from a bottom face 12 b of the working portion 16 ofthe lever body 12. At a distal end of lever body 12 there is provided adistal tip 20. Distal tip 20 is raised to extend above the top face 12 aof the lever body 12. In the embodiments shown, the distal tip 20 curvesupwardly from the working portion 16 at the distal end of the lever body12.

The osteotome 10 preferably has a thin, narrow lever body 12 sized to beinserted into a pre-resection narrow joint space. The lever body 12 maybe between 1-3 mm thick at the working portion 16, and in a preferredembodiment is no more than 2 mm thick. In some preferred embodiments,the thickness of the working portion 16 tapers towards the distal tip 20to no more than 1 mm thick at the tip 20. The width of the workingportion 16 may be between 10-22 mm wide to accommodate compartments ofvarious sizes, and in a preferred embodiment is approximately 15 mmwide.

Referring to FIG. 4, it is shown that the fulcrum 18 is configured torest on a first bone of a joint. The embodiments of the jointdistraction device are depicted and described herein as being used in aknee joint, though it should be understood that the joint distractiondevice may be used in any joint that is suitable for a joint distractionprocedure. Thus, in the figure, the fulcrum is shown resting on a tibialplateau 31 of a patient's tibia 30. This provides the support for theosteotome 10 and the point around which the torque is applied and thedistraction force will be provided to the distal end of the patient'sfemur 40 through distal tip 20. As depicted in FIG. 4, as an externalforce is exerted on the handle portion 14 of the lever body 12, a torqueis applied to the lever body 12 about the fulcrum 18. A resulting forceis then applied at the distal tip 20 which causes the distraction of thejoint, that is, for example, the separation of the first bone (tibia 30)from the second bone (femur 40).

The joint distraction device according to various embodiments isdependent on the force being applied at two known locations: the fulcrum18 and the distal tip 20. To ensure that forces are being applied onlyat these two locations, the fulcrum 18 and the tip 20 project from thebottom face 12 b and the top face 12 a, respectively, of lever body 12such that the lever body 12 does not inadvertently contact either boneof the joint.

As such, the fulcrum 18 is designed to project from the bottom face 12 bto a distance sufficient to prevent contact of the bottom face 12 b withthe tibia 30 during use. In a preferred embodiment, the fulcrum 18extends proud of the body 12 by at least 2 mm, but may be anywherebetween 1-3 mm proud of the body 12, or more. In certain embodiments,the widest portion of the fulcrum 18 is between 4-8 mm, and the thickestportion is between 1-2 mm. The fulcrum may be instrumented such that thefulcrum itself is configured to measure the load being applied at thefulcrum. In such an embodiment, an instrumented fulcrum can be attachedto a standard osteotome to achieve certain features of the disclosedembodiments without further modification to force measuring aspects ofthe osteotome. As shown in the embodiment of FIGS. 2A and 3A, thefulcrum 18 a shape may be somewhat tapered or sharp into a pointed tipto allow slight penetration into bone and/or cartilage to providestability of the osteotome 10 during distraction and while the jointposes are being captured.

In the embodiment shown in FIGS. 2B, 2C, and 3C, the fulcrum is atriangular pad 18 c. The triangular pad 18 c may be connected to thelever body at a rotatable pivot joint. The triangular pad 18 c providesgreater surface in contact with the bone to minimize penetration intothe bone when such penetration would be detrimental or undesirable.Though the pad shown in FIGS. 2B, 2C, and 3C is triangular, otherconfigurations having a narrow top portion to form a portion of a pivotjoint, and a wider bottom portion to contact the bone can be used toprovide a pivot pad for pivoting of the lever body about the fulcrum. Inother embodiments, such as that shown in FIG. 3B, the fulcrum is alinear fulcrum 18 b extending laterally across the lever body 12. Thisembodiment also provides a greater surface area in contact with the boneand may also reduce the penetration of the fulcrum into the bone duringuse.

The distraction force, and thus the measurement of the distraction forceapplied through the distal tip 20 (to be discussed in detail below), issensitive to fulcrum 18 to lift point (tip 20) distance. When thedistance from the fulcrum 18 to the raised tip 20 is known or selected,which it will be when the joint distraction lever is used, the applieddistraction force can be calculated. The fulcrum 18 to tip 20 distancemay be fixed or may be variable and/or adjustable. In a fixed fulcrum totip embodiment, the spacing may be between 10-25 mm. An adjustabledistance embodiment may allow for a greater range of the fulcrum to tipdistance. FIG. 3C depicts an embodiment wherein the fulcrum 18 to tip 20distance can be adjusted by moving the pivot joint along slot 19 andsecuring it at a desired distance from tip 20. In certain preferredembodiments, the distance between the fulcrum 18 and the tip 20 is fixedat 20 mm. This distance is particularly useful for distraction of theknee joint, as it allows the fulcrum 18 to rest on the anterior plateau31 of the tibia 30 and the tip 20 to be directly below the femoralcondyle 41.

Referring to FIGS. 2 and 4-7, it is shown that the distal tip 20projects above the top face 12 a of the lever body 12. In theembodiments shown, the distal tip 20 of the working portion 16 curvesupward to form distal tip 20. Again, in order that forces are applied tothe bones of the joint only at the fulcrum 18 and distal tip 20, thedistal tip 20 is configured such that the top face 12 a of the leverbody 12 does not contact the femur 40 during distraction of the joint.The raised tip 20 may stand 1-5 mm proud of the top face 12 a of thelever body 12, and in a preferred embodiment is curved to be 4 mm proudof the body 12. As shown in the embodiment of FIGS. 2, 4, 5, and 7, thelever body 12 may taper towards the distal tip 20, such that distal tip20 is pointed. The pointed tip, in a preferred embodiment, has a widthof about 1 mm.

The profile of the lever body 12, particularly the distal tip 20, maytake on various profiles, not limited to the pointed distal tip shown inthe previous embodiments. In one exemplary configuration, such as thatshown in FIG. 6, the distal tip 20 takes on the shape of a plate 20 a.The shape may be slightly curved to fit with the outer surface of thebone. In some embodiments, the plate 20 a at the distal tip isspecifically configured for a particular bone or the anatomy of aparticular patient. This configuration provides greater contact surfacearea for torque transmission efficiency as well as to reduce penetrationof the bone being distracted. Other configurations of the distal tip mayalso be used in accordance with additional embodiments of the presentinvention.

The joint distraction lever may have a rotatable handle portion 14. Therotatable handle 14 may allow for a reduction in the amount of torqueworking laterally during joint distraction. For example, whendistracting the knee joint, it is intended to provide the distractionforce substantially parallel with the mechanical axis of the joint.However, the surgeon may not be able to achieve exact access and grip onthe tool such that all forces are being applied in this direction. Sometorque, instead, may be applied sideways on the joint while also beingapplied in parallel with the mechanical axis. The rotatable handle 14may counteract some of the sideways torque applied by cooperating withthe twisting that may occur on the handle when the force is applied atthe handle 14.

The joint distraction lever, such as osteotome 10, is configured tomeasure and provide output related to the distraction force applied tothe bone of the joint, such as the distal femur 40, by the distal tip 20during a distraction procedure. The distraction force is measured by aforce measurement device. The embodiment of FIG. 1 shows a mechanicalforce measurement osteotome. In this embodiment, the lever body 12includes a cut out portion forming a cantilever beam 8. Upon applicationof an applied force, the cantilever bean 8 tilts upward (as depicted inFIGS. 2C and 4). The cantilever beam 8 may be used to determine theapplied force based on its relationship with a reference feature. Forexample, as shown in FIGS. 2C and 4, the cantilever beam 8 may movetowards alignment with tab 9 extending from the handle 14. The jointdistraction lever can be configured such that alignment of thecantilever beam is with the tab 9 indicates a predetermined force value.

Another non-electronic configuration for determining the distractionforce applied at the distal tip 20 is an analog torque wrench that isconfigured to apply a set specific torque to the wrench body or,particularly, lever body 12. Analog graduations of torque settings maybe available, and once determined and set, the lever body 12 will beconfigured to apply a torque and thus cause a distraction force at thedistal tip 20 until a predetermined, desired force is applied. When thepreset torque has been met, the wrench, or lever, is configured toindicate that the preset torque has been reached, or otherwise preventfurther torque from being applied through the lever body.

In another exemplary embodiment, the force measurement device is astrain gauge. One or more strain gauges may be coupled with the leverbody 12 and configured to receive an input voltage provided by a powersource. In certain embodiments, the power source is a battery. Thebattery may be disposable, rechargeable, or take the form of achargeable capacitor. As the electrical conductor of the strain gaugedeforms, as the joint distraction lever deforms as the torque is appliedto distract the bones of the joint, the electrical resistance of theelectrical conductor of the strain gauge changes. Thus, from themeasured electrical resistance of the strain gauge(s), computed usingthe known or measured input voltage and measured output voltage, theamount of applied stress to the joint distraction lever can be measuredand the distraction force computed. A plurality of strain gauges may bearranged and included in the joint distraction lever to form a loadcell. The output of the load cell transducer can then be used to convertthe force or stress determined by the strain gauges into an electricalsignal.

Other mechanisms or tools for measuring the distraction force applied bythe joint distraction lever at the distal tip 20 include piezoelectricpressure sensors wherein a charge is generated when a piezoelectriccrystal, or other suitable material, of the pressure sensor is stressed.The charge output, or the charge output converted to a voltage signal,for example, may be used to compute and indicate the distraction forcebeing applied by the distraction lever. Similarly, stress to the leverbody 12 to compute the distraction force applied at the distal tip 20can be determined using optical sensors in a cantilever beamconfiguration. The optical sensors may include an array of opticalfibers capable of providing computation of stress and strain by way ofwavelength variations between the light source and a detector caused bymodifications in the optical fiber body. Finally, a magnetic contactswitch may be used to indicate the presence of a load being applied, orcan be configured to indicate how much load is being applied.

Referring to FIGS. 7A-7C, osteotome 10 includes an indicator 22. Theindicator 22 provides feedback to a user related to the distractionforce being applied to a first bone of the joint, such as the distalfemur, at the distal tip 20. The feedback may indicate the current valueof the force being applied, or it may be representative of a particularrange of force values, i.e. provide feedback when a predetermined forcevalue has been reached or exceeded. The feedback provided via indicator22 allows for consistent, repeatable, trainable force application.Distinct from prior methods and systems for joint distraction whereforce is subjective, changes between surgeons, and is difficult tolearn, the joint distraction lever according to the disclosedembodiments provides feedback to the user such that consistent force canbe quantified and applied uniformly among different surgeons, betweenone distraction procedure and the next, and can be applied at anyflexion angle. In certain embodiments, the osteotome 10 is configured toapply a force of 85N+/−15N. Accordingly, the indicator 22 is configuredto provide feedback to the user when the distraction force achieves somepredetermined relationship with the desired force value.

FIGS. 7A-7C depict osteotome 10 having an indicator 22 according to apreferred embodiment, wherein the indicator 22 is a light-emitting diode(LED) 24. As shown in FIG. 7A, the LED 24 is in a first illuminationstate as a first range of distraction force is being applied. Forexample, as the osteotome 10 is first inserted in the joint space and noforce is being applied, or only a low amount of force is being applied,the LED 24 may emit light of a certain color, or remain off. FIG. 7Bdepicts the LED 24 in a second state once the distraction force hasachieved or passed a certain predetermined value. For example, thesecond illumination state may cause the LED to emit light of a secondcolor. In an exemplary embodiment, the second state may occur when thedistraction force reaches 70N+/−5N. Finally, FIG. 7C depicts the LED 24in a third illumination state, indicating to the user the apredetermined, desired distraction force, or a maximum distractionforce, has been achieved. For example, the LED may emit light of a thirdcolor once the predetermined force has been reached. In an exemplaryembodiment, the third state may occur when the distraction force reaches100N+/−5N. Alternatively, the LED may provide other illumination statessuch as a slow or rapid flashing state to provide an indication that apredetermined force has been reached.

Some embodiments may use a plurality of LEDs. For example, when anyforce is applied, a first LED may illuminate. Additional LEDs mayilluminate successively as the force increases, each illuminating oncethe force meets a predetermined value. The desired distraction force maybe indicated when all of the LEDs on the lever are illuminated.

Similarly, instead of an LED 24, the indicator 22 may provide feedbackin the form of a sound emitted from the osteotome, such as a beep orclick, or arrangement thereof indicating, for example, a first, second,and third state. Alternatively, the osteotome 10 may provide a singlebeep, click, or other sound only when the desired, predetermined forcevalue has been reached. Likewise, the indicator 22 may provide feedbackin the form of haptic vibration of the joint distraction lever. As withthe LED 24 and the sound indicator, the haptic vibration may indicate toa user various of ranges of distraction force being achieved, or providefeedback only at the desired, predetermined distraction force value.

In the mechanical embodiment of FIG. 1, the indicator is the movement ofthe cantilever beam 8 above the top face 12 a of the working portion 16,relative to the height of the reference tab 9 extending from the handleportion 14. In an embodiment wherein the force computation occurs by ananalog torque wrench, the indicator 22 is the analog graduationsprovided. In electronic embodiments, the output of the various strainsensors may be converted into a signal to display a digitalrepresentation of the force value on a display window on the lever body12 itself or on a display or indicator device coupled thereto. Thedevice may further be configured to communicate the computed forcewirelessly with an external system which may display the force value ona display device or provide the sound feedback or other indicator to theuser of the forces being applied by the joint distraction lever.

In some embodiments, the joint distraction lever may have a presettarget distraction force value, and/or preset force values representingthe various force stages. In such embodiments, the various indicatorsindicate when the preset value is reached. In other embodiments, thejoint distraction lever may be adjustable. In this way, the surgeon mayset the output, i.e., the feedback provided by the indicator, for aselected amount of force. In one example, the surgeon may use the jointdistraction lever to first distract the joint. When the surgeon isapplying the necessary and desired amount of force to cause distractionof the joint, he or she can set that as the force value that generates acertain output, for example, the force that causes the LED toilluminate. In this way, the same load can be applied consistently andrepeatedly by applying a force until that output is again observed. Inone exemplary embodiment, shown in FIG. 4, a dial with value hashtagscan be adjusted to set the force value and output according to thesurgeon's desired load. In other embodiments, an adjustment of thedesired or predetermined values can be adjusted via software implementedin the joint distraction lever and/or with the surgical system 900(described below). Also, referring to FIG. 3C described above, thedistance between the fulcrum and tip can be adjusted such that thedoctor can adjust the distraction force without adjusting his or herapplied force.

Referring to FIG. 8, a method 800 for performing joint distraction usinga joint distraction lever according to the preferred embodiments isdepicted. In step 801, a joint, such as the knee joint including thetibia and the femur, is moved into a first flexion position. In apreferred method, the first flexion position is full flexion though anyrange of flexion may be used. In step 802, a joint distraction leveraccording to the exemplary embodiments disclosed herein is inserted intothe space between the first and second bones of the joint. An externalforce may then be applied to the handle portion 14 of the lever body 12to cause a torque on the joint distraction lever (step 803). In step804, the user receives feedback related to the amount of distractionforce being applied to the first or the second bone of the joint at thedistal tip 20 of the joint distraction lever, as measured by the jointdistraction lever. In step 805, the user, having achieved and having adesired awareness of the distraction force being applied maintains theforce to the handle portion 14 to complete the joint distractionprocedure.

Optionally, after step 805, a pose of the first and second bones of thejoint is captured when the predetermined distraction force is appliedand maintained at the distal tip (step 806). Capturing the pose of thefirst and second bones in the distracted joint assists with surgicalplanning to ultimately attain the desired, properly aligned jointpost-resection and post-prosthetic implantation. To provide forcapturing the pose of the joint, it is contemplated that the exemplaryjoint distraction lever may be used in conjunction with anatomynavigation systems and methods, which may further be used with asurgical system, such as that depicted in FIG. 9. The figure shows anembodiment of a surgical system 900 that includes a computing system920, a surgical tool, such haptic device 930, and a tracking system 940.In operation, the surgical system 900 enables comprehensive surgicalplanning which may include performing distraction of a joint using theosteotome 10 described herein.

Determining the pose of the first and second bones in step 806 may makeuse of tracking system 940. The tracking (or localizing) system 940 ofthe surgical system 900 is configured to determine a pose (i.e.,position and orientation) of one or more objects during a surgicalprocedure to detect movement and capture poses of the object(s). Forexample, the tracking system 940 may include a detection device 941 thatobtains a pose of an object with respect to a coordinate frame ofreference of the detection device. As the object moves in the coordinateframe of reference, the detection device tracks the pose of the objectto detect (or enable the surgical system 900 to determine) movement ofthe object. Tracked objects may include, for example, tools/instruments,patient anatomy, implants/prosthetic devices, and components of thesurgical system 900. Using pose data from the tracking system 940, thesurgical system 900 is also able to register (or map or associate)coordinates in one space to those in another to achieve spatialalignment or correspondence (e.g., using a coordinate transformationprocess as is well known). Objects in physical space may be registeredto any suitable coordinate system, such as a coordinate system beingused by a process running on the computer 921. For example, utilizingpose data from the tracking system 940, the surgical system 900 is ableto associate the physical anatomy with a representation of the anatomy(such as an image displayed on the display device 945). Based on trackedobject and registration data, the surgical system 900 may determine, forexample, (a) a spatial relationship between the image of the anatomy andthe relevant anatomy. Additionally, by tracking the relevant anatomy,the surgical system 900 can compensate for and ascertain movement of therelevant anatomy during the surgical procedure, as needed for capturingthe pose of the distracted joint at the flexion position.

Registration may include any known registration technique, such as, forexample, image-to-image registration (e.g., monomodal registration whereimages of the same type or modality, such as fluoroscopic images or MRimages, are registered and/or multimodal registration where images ofdifferent types or modalities, such as MM and CT, are registered);image-to-physical space registration (e.g., image-to-patientregistration where a digital data set of a patient's anatomy obtained byconventional imaging techniques is registered with the patient's actualanatomy); and/or combined image-to-image and image-to-physical-spaceregistration (e.g., registration of preoperative CT and MRI images to anintraoperative scene).

The tracking system 940 may also be used to track the anatomy and thejoint distraction lever, or osteotome 10, while applying the distractionforce. By tracking the pose (position and orientation) and the movementof the osteotome 10 and the anatomy, the computing system 920 candetermine the directional components of the force being produced. Asdescribed above, in addition to the forces acting along the mechanicalaxis, the distraction force may also act in a lateral direction or otherdirection off-axis from the mechanical axis. Tracking of the objects anddetermination of the directional components can allow for adetermination of the amount of force that is off of the intended axis.This can help the surgeon, or the system automatically, to adjust theapplication of force for more efficient load transmission, and/or toreduce any injury or damage that may occur may applying distractionforces in directions that are off of the intended axis.

The tracking system 940 may be any tracking system that enables thesurgical system 900 to continually determine (or track) a pose of therelevant anatomy of the patient and a pose of the tool 935 (and/or thehaptic device 830). For example, the tracking system 940 may comprise anon-mechanical tracking system, a mechanical tracking system, or anycombination of non-mechanical and mechanical tracking systems suitablefor use in a surgical environment. The non-mechanical tracking systemmay include an optical (or visual), magnetic, radio, or acoustictracking system. Such systems typically include a detection deviceadapted to locate in predefined coordinate space specially recognizabletrackable elements (or trackers) that are detectable by the detectiondevice and that are either configured to be attached to the object to betracked or are an inherent part of the object to be tracked. Forexample, a trackable element may include an array of markers having aunique geometric arrangement and a known geometric relationship to thetracked object when the trackable element is attached to the trackedobject, such as the femur 40 and tibia 30 of a patient. The markers mayinclude any known marker, such as, for example, extrinsic markers (orfiducials) and/or intrinsic features of the tracked object. Extrinsicmarkers are artificial objects that are attached to the patient (e.g.,markers affixed to skin, markers implanted in bone, stereotactic frames,etc.) and are designed to be visible to and accurately detectable by thedetection device. Intrinsic features are salient and accuratelylocatable portions of the tracked object that are sufficiently definedand identifiable to function as recognizable markers (e.g., landmarks,outlines of anatomical structure, shapes, colors, or any othersufficiently recognizable visual indicator). The markers may be locatedusing any suitable detection method, such as, for example, optical,electromagnetic, radio, or acoustic methods as are well known. Forexample, an optical tracking system having a stationary stereo camerapair sensitive to infrared radiation may be used to track markers thatemit infrared radiation either actively (such as a light emitting diodeor LED) or passively (such as a spherical marker with a surface thatreflects infrared radiation). Similarly, a magnetic tracking system mayinclude a stationary field generator that emits a spatially varyingmagnetic field sensed by small coils integrated into the tracked object.

In one embodiment, as shown in FIG. 9, the tracking system 940 includesa non-mechanical tracking system. In this embodiment, the non-mechanicaltracking system is an optical tracking system that includes a detectiondevice 941 and at least one trackable element (or tracker), such asanatomy tracker 943, configured to be disposed on (or incorporated into)a tracked object and detected by the detection device 941. The trackeris configured to be affixed to the tracked object in a secure and stablemanner and includes an array of markers having a known geometricrelationship to the tracked object. The markers may be active (e.g.,light emitting diodes or LEDs) or passive (e.g., reflective spheres, acheckerboard pattern, etc.) and preferably have a unique geometry (e.g.,a unique geometric arrangement of the markers) or, in the case ofactive, wired markers, a unique firing pattern. In operation, thedetection device 941 detects positions of the markers, and the uniquegeometry (or firing pattern) and known geometric relationship to thetracked object enable the surgical system 900 to calculate a pose of thetracked object based on the positions of the markers.

As stated above, a virtual representation of the anatomy, such as theknee joint, can be displayed on display device 945. The display device945 may also display the distraction force measurement obtained by theforce measurement lever. The osteotome 10 may communicate wirelessly orvia a coupled connection with the surgical system 900, or othercomputing or display system, to provide the distraction forcemeasurement for display on an external device, such as the displaydevice 945.

Computing system 920 may be configured to acquire and use the dataobtained during a joint distraction procedure to complete a surgicalplanning procedure. Thus, computing system 920 may capture and store thepose of the first and second bones of the joint via information providedby tracking system 940. The captured pose of the joint may be used toplan bone resection and prosthetic implant placement for proper jointbalance and alignment. The computing system 920 of surgical system 900may be further configured to define a surgical plan based on thecaptured pose(s) of the distracted joint. The computing system 920 thenallows surgical system 900 to implement the surgical plan using thetracking system 940 to, for example, track the pose of a surgical toolrelative to the patient's anatomy, and may also provide haptic feedbackthrough haptic device 930 having surgical tool 935 based on a hapticboundary created during surgical planning. Haptic device 930 providessurgical guidance to a surgeon in order to keep the surgical tool 935from deviating from the surgical plan created based on the jointdistraction procedure and other aspects of surgical planning.

U.S. Pat. No. 8,010,180, titled “Haptic Guidance System and Method,”granted Aug. 30, 2011, which is hereby incorporated by reference hereinin its entirety, describes an exemplary surgical system with which thepresently described joint distraction lever may be used during a jointdistraction procedure and for bone resection and implant planning.

Referring back to the method depicted in FIG. 8, optionally, after step806, the joint is moved to a second flexion position (step 807) and toany number of additional flexion positions, and the poses are capturedwith the predetermined resection force applied to the joint. In theseposes, with the distraction force applied, the knee joint is in thedesired post-resection final position. After collection of poses, boneresection, implant positioning, and implant characteristics are plannedso as to maintain this relative alignment by making the femoral andtibial components contact (or be slightly gapped to allow for somelaxity). Once the bone is resected at this desired plan and the trialsand/or implants are secured to the bone, the leg will then be in thedesired pre-resected posed positions.

Various exemplary embodiments of the invention are described herein.Reference is made to these examples in a non-limiting sense. They areprovided to illustrate more broadly applicable aspects of the invention.Various changes may be made to the invention described and equivalentsmay be substituted without departing from the true spirit and scope ofthe invention. In addition, many modifications may be made to adapt aparticular situation, material, composition of matter, process, processact(s) or step(s) to the objective(s), spirit or scope of the presentinvention. Further, as will be appreciated by those with skill in theart that each of the individual variations described and illustratedherein has discrete components and features which may be readilyseparated from or combined with the features of any of the other severalembodiments without departing from the scope or spirit of the presentinventions. All such modifications are intended to be within the scopeof claims associated with this disclosure.

The invention includes methods that may be performed using the subjectdevices. The methods may include the act of providing such a suitabledevice. Such provision may be performed by the end user. In other words,the “providing” act merely requires the end user obtain, access,approach, position, set-up, activate, power-up or otherwise act toprovide the requisite device in the subject method. Methods recitedherein may be carried out in any order of the recited events which islogically possible, as well as in the recited order of events.

Exemplary aspects of the invention, together with details regardingmaterial selection and manufacture have been set forth above. As forother details of the present invention, these may be appreciated inconnection with the above-referenced patents and publications as well asgenerally known or appreciated by those with skill in the art. The samemay hold true with respect to method-based aspects of the invention interms of additional acts as commonly or logically employed.

In addition, though the invention has been described in reference toseveral examples optionally incorporating various features, theinvention is not to be limited to that which is described or indicatedas contemplated with respect to each variation of the invention. Variouschanges may be made to the invention described and equivalents (whetherrecited herein or not included for the sake of some brevity) may besubstituted without departing from the true spirit and scope of theinvention. In addition, where a range of values is provided, it isunderstood that every intervening value, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range, is encompassed within the invention.

What is claimed is:
 1. A method for performing joint distraction,comprising: moving a joint comprising a first bone and a second boneinto a first flexion position; inserting a joint distraction lever intoa space between the first bone and the second bone, wherein the jointdistraction lever comprises: a lever body having a handle portion and aworking portion; a fulcrum extending from a bottom surface of theworking portion of the lever body; a distal tip, wherein the distal tipis raised above a top surface of the working portion of the lever body;a force measurement device configured to measure a distraction forceapplied at the distal tip during a distraction procedure when a torqueis applied by an external force applied on the handle portion of thelever body; and an indicator configured to demonstrate the distractionforce applied at the distal tip, as measured by the joint distractionlever; applying a force to the handle portion of the lever body of thejoint distraction lever to cause the torque on the joint distractionlever; and receiving feedback from the indicator related to thedistraction force being applied to the first bone at the distal tip asmeasured by the joint distraction lever.
 2. The method of claim 1,further comprising: maintaining the external force to the handle portionwhen a predetermined amount of distraction force is indicated by theindicator; and capturing a pose of the first bone and the second bone atthe first flexion position when the predetermined amount of distractionforce is being applied to the first bone at the distal tip, as indicatedby the indicator.
 3. The method of claim 2, further comprising movingthe joint into a second flexion position and capturing the pose of thefirst bone and the second bone at the second flexion position.
 4. Themethod of claim 1, wherein the indicator provides feedback indicatingthat a predetermined amount of distraction force is being applied. 5.The method of claim 1, wherein receiving feedback comprises observingthe indicator change from a first state to a second state to indicate apredetermined force value has been reached.
 6. The method of claim 1,further comprising tracking, using a tracking system, a pose of thefirst bone, the second bone, and the joint distraction lever todetermine directional components of the distraction force being applied.7. A method for assessing a joint, comprising: inserting a jointdistraction lever into a space between a first bone and a second bone ofthe joint; distracting the joint with the joint distraction lever;determining, using a measurement device of the joint distraction lever,a distraction force applied by the joint distraction lever as the jointdistraction lever is used to distract the joint; determining whether thedistraction force matches a predetermined amount of the distractionforce; and in response to determining that the distraction force matchesthe predetermined amount of the distraction force, capturing first posesof the first bone and the second bone.
 8. The of claim 7, whereincapturing the first poses of the first bone and the second bone isperformed with the joint at a first flexion position, the method furthercomprising: moving the joint to a second flexion position; and inresponse to determining that the distraction force matches thepredetermined amount of the distraction force with the joint in thesecond flexion position, capturing second poses of the first bone andthe second bone.
 9. The method of claim 7, wherein capturing the firstposes of the first bone and the second bone comprises determiningpositions of a first trackable element coupled to the first bone and asecond trackable element coupled to the second bone with a detectiondevice of a tracking system.
 10. The method of claim 7, furthercomprising planning a bone resection for the first bone or the secondbone using the first poses of the first bone and the second bone. 11.The method of claim 7, wherein determining whether the distraction forcematches the predetermined amount of the distraction force comprisesdetermining whether the distraction force is has a value of 100N+/−5N.12. The method of claim 7, wherein distracting the joint with the jointdistraction lever comprises: engaging the first bone with a distal tipof the joint distraction lever; engaging the second bone with a fulcrumof the joint distraction lever, the fulcrum positioned between thedistal tip of the joint distraction lever and a handle portion of thejoint distraction lever; applying an external torque to the handleportion of the joint distraction lever to cause the distraction force tobe exerted between the distal tip at the first bone and the fulcrum atthe second bone.
 13. A method of operating a surgical system,comprising: tracking, by a tracking system, a first bone and a secondbone; measuring, by a distraction lever, a distraction force appliedbetween the first bone and the second bone by the distraction lever;providing an indication relating to a measurement of the distractionforce; while the distraction lever measures the distraction force,capturing, by the tracking system, first relative poses of the firstbone and the second bone; and completing a surgical planning procedureusing the first relative poses of the first bone and the second bonecaptured while the distraction lever measured the distraction force. 14.The method of claim 13, wherein completing the surgical planningprocedure comprises planning prosthetic implant placement whiledetermining a joint alignment based on the first relative poses.
 15. Themethod of claim 13, wherein completing the surgical planning procedurecomprises planning a bone resection while determining a joint balancebased on the first relative poses.
 16. The method of claim 13, whereincompleting the surgical planning procedure comprises generating asurgical plan, and wherein the method further comprises controlling arobotic device to facilitate execution of the surgical plan.
 17. Themethod of claim 13, further comprising distracting, by the distractionlever, the first bone away from the second bone by: engaging the firstbone with a distal tip of the distraction lever; engaging the secondbone with a fulcrum of the distraction lever, the fulcrum positionedbetween the distal tip of the distraction lever and a handle portion ofthe distraction lever; and causing the distraction force to be exertedbetween the distal tip at the first bone and the fulcrum at the secondbone in response to a torque applied the handle portion of thedistraction lever.
 18. The method of claim 13, wherein measuring thedistraction force comprises measuring, by a strain gauge, a torque alonga body of the distraction lever.
 19. The method of claim 13, whereinmeasuring the distraction force comprises computing a stress or strainbased on wavelength variations between a light source and a detectorcaused by modifications in an optical fiber body included with thedistraction lever.
 20. The method of claim 13, wherein providing theindication relating to the measurement of the distraction forcecomprises indicating whether the measurement of the distraction forcematches the predetermined amount of force by controlling a light sourceof the distraction lever.